Method for making flexible tubular members



Oct. 23, 1962 R. H. HART ETAL METHOD FOR MAKING FLEXIBLE TUBULAR MEMBERS Filed March 31, 1960 2 Sheets-Sheet l I I I D U J aw FIG. I.

S m T m. MA L D. F w W E L m H H T R E B 0 R DAN W. THOMAS, JAMES E. RHINEHART ATTORNEY Oct. 23, 1962 R. H. HART ETAL METHOD FOR MAKING FLEXIBLE TUBULAR MEMBERS Filed March 31, 1960 2 Sheets-Sheet 2 FIG].

INVENTORS T, LEWIS F. PLATT,

ROBERT H. HAR

ES E. RHINEHART M M A M o H T W N A D FIG.8.

ATTORNEY United States Patent 3,059,319 METHOD FOR MAKING FLEXIBLE TUBULAR MEMBERS Robert H. Hart, Beloit, Wis., and Lewis F. Platt, Atlanta, Dan W. Thomas, Decatur, and James E. Rhinehart, Atlanta, Ga., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Mar. 31, 1960, Ser. No. 19,133 3 Claims. (Cl. 29-155) The present invention relates to a process for making tubular support members and more particularly for expanding tubular support members composed of two superposed flat strips of metal bonded along their margins and containing an unbounded potential tubular central portion. More specifically, the present invention is directed to the production of flexible support members of the type comprising the subject matter of patent application Serial No. 848,879 filed 26 October 1959, now Patent No. 3,032,151, granted May 1, 1962 to Robert L. Allen and Robert H. Hart, said Hart being one of the present joint inventors.

As described in said patent application, a support member which is transversely rigid, torsion resistant and has an inherent tendency to assume a rectilinear state comprises an elongated tubular member of lenticular cross section having integral fins extending laterally in the plane of its longitudinal edges and being constructed of thin spring material. Such a member when constrained in a coil stores spring energy which is available to uncoil the member to straight form when the constraint is relaxed.

An object of the present invention is to provide a simple effective method for expanding into tubular form a blank composed of two superposed flat strips of sheet spring material joined along their margins.

In practicing the invention, two flats strips of spring tempered metal or equivalent material are superposed and bonded as by welding along their margins. It is im portant that the breadth dimension between the welded margins be constant along the length of the strips. It is also important that the welded strips be flat and if the welding operation shortens the margins the welded strips should be rolled in such a manner that the rolling action on these margins returns them to the length of the unwelded portion of the strips. If the material in the welded area elongates during welding then the rolling action will be applied to increase the length of the unwelded portion. In either event the rolling operation should result in a welded blank which will lay flat without distortion. Since in most metals the welding action will cause shortening, a suitable countermeasure consists in mechanically compressing the strips at the weld area prior to welding whereby the welding will shrink this area to the desired length. The result of the above operation is a flat ribbon composed of a pair of mated strips of spring tempered metal bonded along their longitudinal margins and containing a longitudinally extending unbonded potential tubular intermarginal portion. This flat ribbon is then subjected to a shaping operation which includes progressively decreasing the breadth dimension in such a manner as to expand the unbonded portion outwardly and obtain opposing camber.

Other objects and advantages of the invention will become apparent from the following description when read in connection with the accompanying drawings in which:

FIG. 1 is a view in perspective of bonded strips formed preliminary to the expanding operation;

FIG. 2 is a fragmentary View in perspective showing a preferred form of an apparatus for practicing the invention;

FIG. 3 is a plan view of the apparatus of FIG. 2;

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FIG. 4 is a perspective view of a segment of a tubular member as expanded by the apparatus of FIG. 2;

FIG. 5 illustrates a method of increasing the camber of the expanded tube of FIG. 4;

FIG. 6 illustrates the tube resulting from the operation shown in FIG. 5;

FIG. 7 illustrates the preferred shape of an expanded tubular member;

FIG. 8 is a partial sectional view of the apparatus of FIG. 3 taken at the section 88; and

FIG. 9 illustrates a method of removing excess camber of the expanded tube of FIG. 6.

In practicing the invention two flat strips 10 of spring tempered material, preferably spring steel, are superposed and bonded along their longitudinal margins 11 as by welding, care being taken that the resulting composite ribbon 12 remains flat or if needed is flattened by suitable rolling action after the welding step. The unbonded center portion of the composite ribbon 12 constitutes a potential tubular portion which according to the invention is expanded by progressively subjecting the outer edges of the ribbon 12 to sufficient pressure to decrease its breadth dimension in such a manner that the unbonded central portion of the upper and lower strips 10 part in the center and obtain opposing camber as shown inFIG. 4. An apparatus for accomplishing this expanding operation is shown in FIGS. 2 and 3 as comprising a plurality of shoe 13 mounted along the outer periphery of endless roller chains 14 and 15 trained over pairs of sprocket wheels 16 and 17, respectively. The shoes 13 are provided with slots 18 alined parallel with the chains 14 and being just wide enough to receive the margins of the ribbon 12. The pairs of sprockets 16 and 17 are arranged so that the slotted shoes 13 at what is to be the entrance end is slightly greater than the width of the ribbon 12 and at the exit end is less than the width of the ribbon 12 by an amount sufficient to expand the two strips 10 to the separation desired. Both chains 14 and 15, preferably backed by tracks 19, are moved in the direction of travel of the ribbon 12 by their respective sprockets 16 and 17 at the exit end, which sprockets are driven in synchronism by-a suitable motor 20. Upon insertion of one end of the flat ribbon 12 in the slots 18 at the entrance end of the shoes 13, the sides of the ribbon 12 are gripped by the slotted shoes 13 and moved through the exit end during which time the edges are forced toward each other causing the unbonded portion of the ribbon 12 to separate and obtain permanent deformation with opposing cambers a shown in FIG. 4. The shoes 13 thus constitute a forming matrix.

The passage of the ribbon 12 through the apparatus of FIGS. 2 and 3 without restraining the thickness dimension to which the ribbon 12 expands results in the strips 10 being sharply curved in the center and rapidly decreasing in curvature out toward the margins as indicated in FIG. 4. When the expanded ribbon 12 is to be used as a flexible support member, it is desirable to move more material away from the neutral axis such as results when the strips 10 have a substantially uniform curvature throughout their width dimension as illustrated in FIG. 7. One method of accomplishing this result is to insert a mandrel such as a hexagonal bar 21 in the void of the expanded ribbon 12 as shown in FIG. 5 and rerunning this assembly through the forming apparatus of FIGS. 2 and 3 which causes bending to occur on both strips 10 parallel to and adjacent to the felded margins 11 which places more: material away from the neutral axis and increases the second moment of area of the section as indicated in FIG. 6. The strip 12 in this condition (FIG. 6) now probably has more camber than may be retained after the member has been flattened. The excess camber is removed by bending the expanded ribbon 12 alternately in both directions around a drum 25 (FIG. 9) having a radius small enough to cause the strips 10 to flatten against each other thereby removing equal amounts of camber from both the strips 10 and resulting in a flexible tubular support member 12 having the sectional configuration substantially as shown in FIG. 7. The drum 25 may be provided with a clip 26 under which one end of the tube 12 is inserted to facilitate the bending operation.

The desired sectional configuration shown in FIG. 7 may be directly obtained in a single forming operation by providing suitable fixed opposed platens 22 having their facing surfaces shaped and spaced to conform to the desired sectional configuration and arranged between the slotted shoes 13 and extending from the exit end thereof toward the entrance end a sufiicient distance to insure that when the ribbon 12 reaches the leading edges of the platens 22 its expanded dimension will be less than the distance separating the opposed platens 22. The facing surfaces of the platens 22 may be shaped and spaced to produce other sectional configurations of the expanded ribbon 12; however, the configuration substantially as illustrated in FIGS. 7 and 8 is preferred for providing flexible support members of the type comprising the subject matter of the above identified patent application filed by Robert L. Allen and Robert H. Hart. This sectional configuration may also be directly obtained by positioning a shaping mandrel 23 within the expanding ribbon 12 and in contact only with the noncentral areas thereof to force more bending adjacent the bonded margins 11 and thus overcome the tendency of the central portion of the ribbon 12 to become too sharply curved.

When the apparatus of PEG. 3 utilizes both the restraining platens 22 and the shaping mandrel 23 it may be desirable to mount the platens 22 and the mandrel 23 so that they yield to a certain pressure to the end that some variation in the dimension of the fabricated composite ribbon 12 may be readily tolerated.

While for the purpose of disclosing the invention the preferred embodiments thereof have been described in detail to enable those skilled in the art to practice the invention it will be evident in view of the above disclosure that various modifications may be made therein without departing from the intended scope of the invention as set forth in the appended claims.

What is claimed is:

1. The method of making an elongated hollow flexible support member of uniform lenticular cross section with integral fins extending laterally in the plane of its longitudinal edges which includes bonding together the longitudinal margins of two superposed fiat rectangular strips of spring tempered metal to provide a flat bonded blank containing an unbonded potential tubular portion, longitudinally advancing the bonded blank while subjecting the same to pressure from opposite edges thereof to progressively decrease its breadth dimension and to expand the unbonded portion outwardly in permanent deformation with opposing cambers, and during such expansion restraining only the outermost expanded surface portions to cause additional expansion of the unbonded portion adjacent the bonded margins.

2. The method of expanding a tubular support member composed of two superposed flat rectangular strips of metal bonded along their margins and containing an unbonded potential tubular portion therebetween, comprising longitudinally advancing said member while subjecting the same to pressure from opposite edges thereof to decrease its breadth dimension and to expand the unbonded portion outwardly in permanent deformation with opposing cambers, inserting a bar mandrel into the expanded portion to increase its breadth dimension, and while said mandrel is so inserted again subjecting said member to pressure from opposite edges thereof to decrease its breadth dimension to expand the unbonded portions adjacent the bonded margins.

3. The method according to claim 2 including the step of alternately bending in opposite directions the expanded member around a drum having a diameter just small enough to cause the strips to flatten against each other and thereby remove any excess camber.

References Cited in the file of this patent UNITED STATES PATENTS 722,398 Bock Mar. 10, 1903 1,037,099 York Aug. 27, 1912 1,947,392 Guntermann et al. Feb. 13, 1934 2,142,443 Goin Jan. 3, 1939 2,569,266 Thompson Sept. 25, 1951 2,889,614 Seely June 9, 1959 

